Process for producing an intensity distribution over a working laser beam and a device for this purpose

Abstract

In a process for producing a stipulated intensity distribution of a working laser beam on an object surface, at least one first and one second component beam with a stipulated first and second intensity distribution are formed and the power of each component beam is changed in a controlled manner with switching times down to submicroseconds. The component beams at a third intensity distribution superimposed as the working beam are pointed at or into the object in order to achieve a different action as a result of a varied third intensity distribution of the working beam. In contrast to conventional processes the first intensity distribution I b =a×f b (x, y, t) differs from the following one I n =a×f n (x, y, t) by the value of the function f u (x, y, t) and no longer only by an altered linear value a. The process as claimed in the invention can be preferably used in the production of screen cells on an engraved cylinder.

What is claimed is:  
     
       1. A process for producing a stipulated intensity distribution of a working laser beam on an object surface or in an object, characterized in that at least one first and one second component beam with a stipulated first and second intensity distribution are formed from only one source beam and the power of each component beam is changed in a controlled manner with switching times in the submicroseconds, and the component beams at a third intensity distribution superimposed as the working beam are pointed at the object surface or into the object in order to achieve a different action as a result of a varied third intensity distribution of the working beam. 
     
     
       2. The process as claimed in  claim 1 , wherein a first beam of a pulsed laser is split with a first acousto-optical modulator into a first and a second component beam with a component power which is adjustable by the first modulator, the first component beam is shaped to a stipulated beam diameter with a stipulated intensity distribution over its cross section, the second component beam is power- modulated with a second acousto-optical modulator and shaped to a likewise stipulated beam diameter with a stipulated intensity distribution which can differ from that or those of the first component beam, the two component beams are combined into a material machining beam and are focussed on the material surface, the location of the radiation focussing is changed according to a stipulated number of pulses of the laser, the local change and the intensity of the first and second component beams being changed in a controlled manner with the two modulators such that on the material surface a series of cells with different aspect ratios is formed so that a surface machined in this way as part of a roller, is used as an engraved cylinder. 
     
     
       3. The process as claimed in  claim 1 , wherein the radiation of all component beams are emitted from the pertinent radiation source and are combined into a single working beam, the combined beam is pointed at the object surface or into the object. 
     
     
       4. The process as claimed in  claim 3 , wherein the radiation of all component beams are emitted coincident in time from the pertinent radiation source. 
     
     
       5. The process as claimed in  claim 3 , wherein the radiation of all component beams are combined at least spatially superimposed in part into said single working beam. 
     
     
       6. The process as claimed in  claim 3 , wherein the radiation of all component beams are combined in part into said single working beam by geometrical superposition. 
     
     
       7. The process as claimed in  claim 3 , wherein said combined beam is pointed focussed at the object surface or into the object. 
     
     
       8. The process as claimed in  claim 3 , wherein said combined beam is pointed at the object surface or into the object and the location in or on the object is continually changed. 
     
     
       9. The process as claimed in  claim 1 , wherein the time power characteristic of the radiation of at least one component beam is changed in a controlled manner in time with switching times in the sub-microseconds. 
     
     
       10. The process as claimed in  claim 1 , wherein the intensity of each component beam is changed by the corresponding electrical triggering of an optical switching means. 
     
     
       11. The process as claimed in  claim 10 , wherein the optical switching means includes an electro-optical or magneto-optical element. 
     
     
       12. The process as claimed in  claim 11 , wherein at least one of said elements of said optical switching means splits the beam into at least two component beams. 
     
     
       13. The process as claimed in  claim 1 , wherein a beam profile of each component beam before their combination is shaped into a given profile in order to obtain the stipulated intensity distribution, the intensity distribution differs fundamentally from that of each individual beam and can be varied with switching times in the sub-microseconds without mechanical movement of the optical components. 
     
     
       14. The process as claimed in  claim 13 , wherein said stipulated intensity distribution is obtained with subsequent focussing and said intensity distrubution differs fundamentally from that of each individual focussed beam. 
     
     
       15. A device for producing an intensity distribution of a working beam on or in an object, comprising: 
       a least one radiation source for generating at least two component beams with a beam splitter,  
       a beam profile shaping unit for at least one of the component beams;  
       at least one power setting means for switching in the sub-microseconds for at least one component beam;  
       a unit for combining the component beams into a working beam; and  
       a positioning means for positioning the working beam.  
     
     
       16. A device as claimed in  claim 15  further comprising focussing means for focussing the working beam onto or into the object. 
     
     
       17. A device as claimed in  claim 15 , wherein the radiation source is a periodically pulsed Q-switch laser for producing a source beam, the beam splitter also acts as the power setting means, with the beam splitter the source beam is dividable into two component beams in a controlled manner such that each component beam per laser pulse has a stipluated power, and another power setting means for setting the power of the radiation of one of the two component beams. 
     
     
       18. A device as claimed in  claim 17 , wherein said beam splitter acts as an acousto-optical modulator. 
     
     
       19. The device as claimed in  claim 15 , further comprising: 
       a control means with a memory, screen information is stored in the memory for the pixels of a gravure screen;  
       an engraved cylinder having a surface which is the workpiece surface to be machined, an electrical connection of the control means is connected to each power setting means for power control of the component beams for each radiation pulse in order to obtain per screen point to be generated on the engraved cylinder, and  
       a predefinable radiation cross section and/or a time intensity profile of the working beam on the workpiece surface is the object surface for material removal with a predefinable aspect ratio.